I own a DM-15 and a DM-42. I also own an HP-12c and like the size and form factor and would like a scientific calculator the same shape/size, but I'm finding it difficult to justify another purchase.

The DM-15 can handle hyperbolic trig, factorials, permutations and combinations. Can the DM-41L?

If the DM-41L has all the functions that the DM-15 has, then is the only additional feature the alpha? The DM-42 has all the features I want, but the wrong form factor. The DM-41L is the right form factor, but I'm curious what it really adds to the DM-15L.

My dilemma: if the DM-41L only really adds alpha to the DM-15L (and the clock, which I don't use much... or maybe I would if I had it), then can I really justify over £120ish for another calculator that adds little more functionality than the DM-15 I already have?

Mmmm, the more I think about it, the more I want to purchase the DM-41L anyway... please help me justify it!!!

There are a few features that the DM15 has and the DM41 does not. An integrator, solver, matrix calculus and complex numbers. I don't think the DM41 does hyperbolic trig either.

What the DM41 does get you is the ability to name programs in the same way you do the DM42. Alpha input is another thing, and a completely user-assignable keyboard. You get 319 registers worth of memory to store programs in main memory and since the V25 update you get 362 registers of extended memory instead of "only" 124.

Look for a manual for the HP-41CX on line, that's what you're getting in a landscape format, plus one extra HP-82181A X-Mem module built in as of firmware V25.

Please note that the DM41 is significantly slower than the DM15 for similar operations. So, if you do need any of the features present in the DM15 and not in the DM41 then use the DM15. A program to replace the feature will not run anywhere near as fast. On the HPMuseum.org forum, someone suggested a form of benchmark using transcendental functions. I ran the benchmarks with my HP-15C, HP-41C, HP-42S, DM15L, DM41L and DM42 among others and got these results:

There are plenty of things that you will be able to do with a 41 but not with a 15. For example, right now I'm writing a program that will allow me to keep track of time that I spend on multiple projects. It uses the time module, of course, and it stores start/stop details of individual projects in data files in X-Mem. There are proper, human-readable prompts thanks to the 41's alpha abilities and input is collected by reading the keyboard with GETKEY. None of that is possible with a DM15...

If you're a bit of a nerd as your recent Facebook post would suggest, then you'll have plenty of fun with the DM41L. Just remember to make liberal use of 'ASN', which assigns functions to keys in USER mode.